Implementing-cryptography-using-python

172 Chapter 6 ■ Using Cryptography with Images
In the following example and the subsequent ones in this chapter, we will be
encrypting the original image and then saving it with an e in front of the name.
When we decrypt the image, we save it with a d in front of the name. The reason
we’re doing this is to be able to compare the original image with the decrypted
image to see if there is any apparent data loss.
Figure 6.1 shows the original image we will use. Feel free to create your own
for this exercise. It is a fairly small file, which is fine until we get to the end of
the chapter. For hiding blob data, you may need a much larger file. Time for a
little code.
Figure 6.1: Original ch6_secret_image.jpg file
print('The program is looking for a file named: ch6_secret_image.jpg')
fo = open("Chapter6\ch6_secret_image.jpg", "rb")
image = fo.read()
fo.close()
print()
print("The secret key is 42.")
image = bytearray(image)
key = 42
for index, value in enumerate(image):
image[index] = value^key
print()
print('The image has been encrypted. Review e_ch6_secret_image.jpg')
fo = open("Chapter6\e_ch6_secret_image.jpg", "wb")
fo.write(image)
fo.close()
image = bytearray(image)
for index, value in enumerate(image):
image[index] = key^value